1. Field of The Invention
The present invention relates, in general, to a composition for preparing an organic insulator. More specifically, the present invention relates to a composition for preparing an organic insulator comprising (i) an organic-inorganic hybrid material, (ii) at least one organometallic compound and/or organic polymer and (iii) a solvent for dissolving components (i) and (ii), and an organic insulator prepared using the same.
2. Description of The Related Art
Thin film transistors (hereinafter, referred to as ‘TFT’s) are frequently used in display devices and consist of a silicon semiconductor film, oxidized silicon insulating film and metal electrodes. Recently, organic TFTs employing semiconducting materials have been developed (U.S. Pat. No. 5,347,114). Such materials have been researched throughout the world due to their promising properties. Specifically, that organic TFTs are flexible and convenient to manufacture accelerate their applications in the area of field display.
Ever since the development of polyacetylene, a conjugated organic polymer that exhibits semiconductor characteristics, there has been vigorous research on organic, polymeric semiconductor materials. Such materials served as the basis for novel electronic devices with many applications in a variety of fields, for example, functional electronic devices and optical devices. This is because organic polymers, when used in an organic semiconductor, show many advantages: they can be synthesized at low cost using a variety of synthetic routes; they can be easily produced into a fiber or film; and, they show excellent flexibility and good conductivity.
As one of many devices prepared using the organic conductive polymers, organic TFTs characterized by the inclusion of an organic polymer as an active film have been studied since the 1980s. In recent years, a lot of research on such organic TFTs has been done all over the world. The organic TFT is similar in structure to a conventional Si-TFT, but it is different in that an organic polymer is used as a semiconductor material instead of silicon. In the process of making an organic TFT, a thin film of semiconductor layer can be fabricated by a printing-process under atmospheric pressure. This process is in contrast with the use of plasma, by chemical vapor deposition (CVD), which is troublesome but essential for the formation of a silicon thin film. Furthermore, for an organic TFT, a continuous roll to roll process using a plastic substrate can be applied so it is possible to provide a transistor at a lower cost.
Generally, organic TFTs are equal or superior to amorphous silicon TFTs in charge carrier mobility, but their driving and threshold voltages are very high. Using amorphous silicon and pentacene, 0.6 cm2/V-sec of charge carrier mobility is expressed (N. Jackson, 54th Annual Device Research Conference Digest 1996), but there are some problems in that the driving voltage is higher than 100 V and the sub-threshold voltage is 50 times of that of amorphous silicon.
There has been quite a bit of research directed to using high k insulators for the purpose of controlling driving voltage and decreasing the threshold voltage, not only in the field of silicon TFTs, but also in the field of organic TFTs (U.S. Pat. No. 5,981,970, Science, Vol. 283, p 822-824, Organic Electronics 3, 65-72). For example, ferroelectric insulating materials such as BaxSr1-xTiO3 (BST), Ta2O5, Y2O3, or TiO2, and inorganic insulating materials having a dielectric ratio more than 15, such as PbZrxTi1-xO3 (PZT), Bi4Ti3O12, BaMgF4, SrBi2(Ta1-xNbx)2O9, Ba(Zr1-xTix)O3 (BZT), BaTiO3 or SrTiO3 have been reported (U.S. Pat. No. 5,946,551). The devices using these materials are coated by either deposition methods (CVD, sputtering or ALD) or sol-gel methods. It is reported that the charge carrier mobility of the devices is less than 0.6 cm2/V-sec and the driving voltage is less than −5V. Still, however, there are restrictions of usage with respect to the various substrates because a high temperature (200˜400° C.) is required in most of manufacturing processes. Also, it is difficult to apply printing-type processes in manufacturing the devices. At present, organic insulating films containing polyimide, BCB (benzocyclobutene), photoacryl, etc., cannot match the properties of inorganic insulators (U.S. Pat. No. 6,232,157).
Recently, many attempts have been made to use organic TFTs for various driving devices. However, to realize the practical use of organic TFTs, not only in liquid crystal displays (LCDs) but also in flexible displays containing organic electroluminescent device, a charge carrier mobility over 10 cm2/V-s is required. Also, in a production process, it is desirable for the insulating film to be coated by an all-printing or all-spin method on a plastic substrate for simplicity and cost reduction. There has been a lot of research directed to organic insulators having a simplified production process and improved charge carrier mobility. The focus has been on providing an advantageous condition for the formation of the organic active layer, thus increasing the grain size of organic active layer in comparison to an inorganic insulating film. Generally, these organic insulating films shows a dielectric ratio of 3-4, which requires 30-50 V of high driving voltage and 15-20 V of high threshold voltage.
To increase dielectric ratio, there has been an attempt to disperse nanometer-sized ferro-electric ceramic particles into an insulating polymer (U.S. Pat. No. 6,586,791). But, there are some problems with that approach. The ceramic particles affect the formation of the organic active layer, and thus decrease charge carrier mobility or increase leakage current. This requires that an additional insulating film having good dielectric properties be used. In this art, therefore, one must develop an organic TFT that shows a high dielectric ratio and superior insulating properties, and that can increase the display of the semiconductor.